1. Field of the Invention
The present invention relates to a dielectric laminated device to be used for the high frequency wireless apparatuses such as portable telephones, and a manufacturing method thereof.
For example, the dielectric laminated resonator as a dielectric laminated device shown herein may be used solely as a resonator element for a high frequency oscillating circuit, and besides, the plural dielectric laminated resonators are used for combining to constitute a dielectric filter which operates as a band pass filter or a band elimination filter.
2. Description of the Related Art
In recent years, with the development of mobile communication, there have been strong demands for miniature portable telephone apparatuses which are convenient to carry with. Especially, because a dielectric filter using a dielectric laminated resonator is one of the most important parts of the high frequency parts to be used for the wireless circuit of the portable telephones, its formation into miniature size and high performance is strongly demanded.
Hereinafter, referring to the drawings, an example of the conventional dielectric laminated resonator as mentioned above is explained. FIG. 19 shows a disassembled perspective view of a conventional dielectric laminated resonator. FIG. 20 shows a sectional view of a plane including the line X-X' in FIG. 19. Further, FIG. 21 shows a sectional view of a plane including the line Y-Y' in FIG. 19.
In FIGS. 19, 20, and 21, a strip line 202 is formed on the first dielectric sheet 201, and the dielectric sheets 201 and 203 which are laminated on the upper and lower parts of the strip line 202, are put between the shield electrodes 204. By grounding an end of the strip line 202 through the grounding electrode 205, a tip short-circuited strip line resonator is constituted. With the frequency at which the length of the strip line becomes 1/4 wavelength, the impedance at the open end becomes infinitive and parallel resonance occurs. The dielectric laminated resonator of such a structure is disclosed, for example, in Japanese Patent Laid-open No. H2-290303, FIG. 1.
However, according to the constitution as described above, it is possible to make the resonator thin and small size, but due to the formation of the strip line by screen printing, it is difficult to form the line thickness to more than 20 .mu., and due to the formation of the convex part by forming a strip line on the dielectric sheet, the edge on the lateral side of the strip line crashes, leading to thinning of the line thickness on the lateral side part of the strip line.
Accordingly, the high frequency current concentrates on the lateral side of the strip line, thereby providing the problems such as enlargement of the conduction loss of the strip line and lowering of unloaded Q.